## Ballistics pendulum on steroids

1. The problem statement, all variables and given/known data

I am doing a science fair experiment using a ballistics pendulum. Instead of a wooden block to fire into I am using ballistics gelatin. This will allow me to measure the amount of energy deposited into the gelatin. A ballistics pendulum is usually used to determine velocity but I want to determine the amount of energy. I can determine velocity using available data. Most of the data on ballistics pendulums indicates the collision is inelastic. I assume this is because all of the energy is deposited into the wooden block. I believe in this instance the collision will be elastic, not perfectly elastic, since the two objects will move independently after the collision. The gelatin will initially move with the bullet but then the bullet will continue on and the gelatin will return to its original position.

2. Relevant equations

KEi= 1/2m vo^2

where m = mass of bullet and vo = the initial velocity of the bullet

KEf = 1/2 (m+M) vf^2

where M = mass of pendulum and vf = velocity of pendulum and ball

PEf = (m+M)(g)(h)

where g = gravitational acceleration
and h = change in height of gel block

3. The attempt at a solution

It seems like I should be able to just use the equation PEf = (m+M)(g)(h) to determine the kinetic energy converted to potential energy in the gel block but the more I read the less sure I am about this. I don't have any data yet as I am just in the research stage. I just need to determine if I'm right about this being an elastic collision and using the PEf equation to determine the amount of energy deposited into the gel.

Maybe, since kinetic energy is being converted to internal energy (in the gel block) and potential energy I can't determine the amount of energy deposited? Maybe, this is conservation of momentum and not conservation of energy? Maybe I'm in over my head!

Help!!!